Currently, movable robots, such as sweeping robots, have been accepted and practically used by more and more families. Commonly-known robot positioning and map building both rely on active emission of signals, such as laser, infrared, etc., to detect the external environment to build a map. For example, some intelligent robots real-time positioning and map building technology are FastSLAM. FastSLAM is typically implemented using a laser rangefinder or sonar. Since FastSLAM uses sensors like a laser or sonar etc., a robot cannot identify in certain circumstances but can only estimate the whole environmental condition by prejudgment.